What does the QRS complex in an ECG signify?

• A. Atrial contraction
• B. Ventricular depolarization, signaling ventricular contraction
• C. Ventricular repolarization
• D. Delay in conduction through the AV node

Answer: (B)

The QRS complex in an ECG represents ventricular depolarization, which is the electrical activity that triggers ventricular contraction. This part of the ECG wave reflects the moment when the heart's ventricles receive electrical stimulation, causing them to contract and pump blood to the lungs and the rest of the body.

In the cardiac cycle, depolarization occurs when sodium ions enter cardiac muscle cells, resulting in a change in electrical charge across the cell membrane. This change initiates the contraction of the ventricles, making the QRS complex a crucial component of the ECG.

Understanding the significance of the QRS complex is fundamental in assessing the heart's electrical function and identifying potential arrhythmias, ischemia, or other cardiac conditions.